add merging_strings_alternatively implementation and update CMakeLists.txt

Easy/merge_strings_alternatively/merging_strings_alternatively.cpp

@@ -0,0 +1,28 @@
+//
+// Created by bob on 02/05/2026.
+//
+
+#include "merging_strings_alternatively.h"
+
+class merging_strings_alternatively {
+public:
+    string mergeAlternately(string word1, string word2) {
+
+        int i = 0;
+        string out = "";
+        int l1 = word1.length();
+        int l2 = word2.length();
+
+        while (i < l1 || i < l2)
+        {
+            if (i < l1){
+                out += word1[i];
+            }
+            if (i < l2){
+                out += word2[i];
+            }
+            i++;
+        }
+        return out;
+    }
+};